Magnetic head gimbal assembly and magnetic disk unit

ABSTRACT

A magnetic disk unit includes a magnetic disk attached to a spindle so as to be rotatable, a slider having a magnetic head for reading/writing data onto/from the magnetic disk, a suspension for providing the slider with a predetermined load, and an actuator arm for positioning the slider attached to the suspension on the magnetic disk. A first pad including the magnetic head and second pads including no magnetic heads are disposed on an air bearing surface of the slider. During rotation of said magnetic disk, a part of the first pad keeps in contact with the magnetic disk. A load point of the suspension with respect to the slider is positioned between a leading edge of the slider and a position located at a distance equivalent to substantially 0.42 times a whole length of the slider from the leading edge of the slider.

This is a division of U.S. patent application Ser. No. 08/628,226, filedon Apr. 4, 1996 now U.S. Pat. No. 6,157,519.

BACKGROUND OF THE INVENTION

The present invention relates to magnetic disk units, and in particularto a magnetic head slider and its suspension structure in a magneticdisk unit of the contact recording type in which a magnetic head slideris brought into contact with a magnetic disk.

In order to increase the recoding density of magnetic disk units, theflying height between a slider for mounting a magnetic head and amagnetic disk has tended to be reduced. As the flying height is reduced,contact between the slider and the magnetic disk is becoming inevitable.Thus, there has been proposed a magnetic disk unit of the so-calledcontact recording type in which magnetic recording is performed with theslider brought into contact with the magnetic disk from the beginning.

In U.S. Pat. No. 5,041,932, there is disclosed an integral magnetichead/suspension structure formed as a long and slender bent dielectricobject or as a suspension having a magnetic head on one end thereof.This integral magnetic head/suspension has a feature of extremely lightmass. By reducing the mass of the integral magnetic head/suspension, theload applied to the magnetic disk can be reduced and wear between themagnetic head/slider and the magnetic disk can be reduced.

In a structure proposed in JP-A-6-251528, the flying force generated bythe air flow caused by rotating the magnetic disk under the integralmagnetic head/suspension assembly is canceled by mounting the suspensionsection so as to form a suitable angle with respect to the surface ofthe magnetic disk and thereby causing a compressive force due to airflow to act. In this structure, the contact state is maintained over theentire surface of the magnetic disk.

In a positive pressure slider of flying/contact mixture type proposed inJP-A-5-74090 and JP-A6-052645, a magnetic head is disposed on a centerrail formed on a trailing edge of a positive pressure slider of a flyingtype, and only the center rail having the magnetic head is brought intocontact with a magnetic disk to conduct magnetic recording.

In a negative pressure slider of the flying/contact mixture typeproposed in JP-A-62-167610, a trailing edge of a negative pressureslider of a flying type is brought into contact with a magnetic disk toconduct magnetic recording.

SUMMARY OF THE INVENTION

An object of the present invention is to reduce, in magnetic disk unitsof the contact recording type, contact force between a slider and amagnetic disk so as not to damage the slider and the magnetic diskfatally.

Another object of the present invention is to provide a magnetic diskunit capable of maintaining uniform contact force over the entiresurface of a magnetic disk and conducting stable contact recording overa long period.

Another object of the present invention is to decrease frictional forcecaused in a contact portion between a slider and a magnetic disk whenthe slider is positioned on a data track on the magnetic disk by anactuator arm to such a degree as not to affect the positioning accuracy.

Still another object of the present invention is to restrict jumping ofa slider from a magnetic disk caused by unsteady contact force, debrison the magnetic disk, or vibration of the magnetic disk unit.

In accordance with a first aspect of an embodiment of the presentinvention, a first pad including a magnetic head and second pads whichdo not include a magnetic head are provided on an air bearing surface ofa slider of a magnetic disk. A part of the first pad keeps in contactwith a magnetic disk when the magnetic disk is rotated, and a load pointis positioned between a leading edge of the slider and a positionlocated at a distance of approximately 0.42 times the whole length ofthe slider from the leading edge of the slider.

In accordance with a second aspect of an embodiment of the presentinvention, a trailing pad including a magnetic head and other pads whichdo not include a magnetic head are provided on an air bearing surface ofa slider of a magnetic disk unit, and only the trailing pad keeps incontact with the magnetic disk while the magnetic disk is being rotatedwhereas other pads are kept apart from and fly over the magnetic diskdue to an air flow caused by the rotation of the magnetic disk, thecontact force between the trailing end pad and the magnetic disk beingat most 200 mgf.

In accordance with a third aspect of an embodiment of the presentinvention, a slider having a magnetic head includes, in its air bearingsurface, a first pair of positive pressure side pads located on theleading side, a second pair of positive pressure side pads locatednearly in the center in the slider length direction, and a positivepressure center pad. Located on the trailing edge side and containingthe magnetic head, the area of the second positive pressure side padsbeing greater than the area of the first positive pressure side pads andthe area of the positive pressure center pad.

In accordance with a fourth aspect of an embodiment of the presentinvention, a first pad including the magnetic head and second padsincluding no magnetic heads are disposed on the air bearing surface ofthe slider, and flying force generated by the first pad is sufficientlysmaller than flying force generated by the second pads. The magnitudeand pressure center of the flying force generated by the second pads issubstantially coincident with the magnitude of the load driven to theslider by the suspension and the load point, and the slider is providedby a gimbal of the suspension with a moment force in such a direction asto make the first pad approach the magnetic disk, only the first padkeeping in contact with the magnetic disk during rotation of themagnetic disk.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view showing the contact state between a slider and amagnetic disk in an embodiment of the present invention.

FIG. 2 is an enlarged view of the slider and the magnetic disk shown inFIG. 1.

FIG. 3 is a top view showing the air bearing surface of the sliderillustrated in FIG. 1.

FIG. 4 is a graph showing the dependence of the normalized wear valueupon the contact force applied between the slider and the magnetic disk.

FIG. 5 is a graph showing dependence of the contact force between theslider and the magnetic disk upon the maximum roughness of the magneticdisk.

FIG. 6 is a graph showing the pressure distribution of the slider.

FIG. 7 is a graph showing dependence of the contact force between theslider and the magnetic disk upon the sum of the mass of the slider andthe equivalent mass of a suspension.

FIG. 8 is a graph showing dependence of the flying height upon theradial disk position in a slider of the present invention andconventional sliders.

FIG. 9 is a graph showing dependence of the normalized contact forceupon the radial disk position in a slider of the present invention andconventional sliders.

FIG. 10A is a side view showing the contact state between a slider and amagnetic disk in another embodiment of the present invention.

FIG. 10B is a graph showing dependence of impulsive force T appliedbetween the slider and a suspension illustrated in FIG. 10A upon adistance x between a leading edge of the slider and a load point.

FIG. 10C is a side view showing the contact state between a slider and amagnetic disk in another embodiment of the present invention.

FIG. 11 is a top view showing an example of an air bearing surface of aslider.

FIG. 12 is a top view showing another example of an air bearing surfaceof a slider.

FIG. 13 is a side view showing the contact state between a slider and amagnetic disk in another embodiment of the present invention.

FIG. 14 is a top view showing an air bearing surface of a slider.

FIG. 15 is a top view showing a magnetic disk unit with a rotaryactuator scheme using a slider of the present invention.

DETAILED DESCRIPTION

Hereafter, an embodiment of the present invention will be described indetail by referring to drawing.

FIG. 1 is a side view illustrating the contact state between a sliderand a magnetic disk in a magnetic disk unit of the mixed flying/contacttype which is a first embodiment of the present invention. Apredetermined load w is applied to a slider 1 by a suspension 2 via aload point A. A magnetic disk 3 is driven and rotated by a spindle (notillustrated). As the magnetic disk 3 is rotated, an air flow isgenerated in a direction represented by an arrow V and it flows into aspace formed between the slider 1 and the magnetic disk 3. This airwhich has flowed into the space between the slider 1 and the magneticdisk 3 is compressed between them, and the leading side of the slider 1flies with flying force f2. The trailing edge of the slider 1 comes incontact with the magnetic disk 3 while generating contact force f2.Furthermore, frictional force f_(cr3) is generated in a contact portionB in a direction opposite to the air inflow direction as shown in FIG.2. Denoting the distance measured from the load point A to the contactportion B located between the slider 1 and the magnetic disk 3 by L1 anddenoting the distance measured from the load point A to a pressurecenter C of the flying force f2 by L2, the slider 1 carries out contactrecording with respect to the magnetic disk 3 in such a posture as tosatisfy the following two equations.

w=f 1+f 2  (1)

f 1·L 1=f 2·L 2  (2)

From these two equations, the contact force f1 is related to the thrustload w by the following equation.

$\begin{matrix}{{f1} = \frac{{L2} \cdot w}{{L1} + {L2}}} & (3)\end{matrix}$

From equation (3), it will be appreciated that the substantial contactforce f1 can be made smaller than the load w in the slider/suspension ofmixed flying/contact type by suitably selecting the relation between thedistance L1 between the load point A and the contact portion B and thedistance L2 between the load action point A and the pressure center C offlying force. On the other hand, in an integral magnetic head/suspensionhaving light mass and a light load, the load point and the contactportion are located nearly on a straight line. Since L1 is thus nearly 0in this case, the load w becomes nearly equal to the contact force f1.Although the contact force f1 can be made less than the load w asexpressed by equation (3) in the slider/suspension of mixedflying/contact type, the flying force between the slider 1 and themagnetic disk 3 increases as the velocity of the magnetic disk 3 isincreased, making it difficult to maintain the stable contact state.Furthermore, according to the study of the present inventors, theslider/suspension and the magnetic disk must satisfy various conditionsfor the magnetic head to maintain the stable contact state over a longtime without causing a fatal fault on the slider 1 and the magnetic disk3. These facts will now be described in detail by referring to FIGS. 2through 4.

FIG. 2 is an enlarged view of contact portions of the slider 1 and themagnetic disk 3. The main body of the slider 1 is made of ceramic suchas Al₂O₃TiC. On the air bearing surface, a slider overcoat including asilicon layer 11 and a carbon layer 12 is formed. The silicon layer 11and the carbon layer 12 are 3 nm and 7 nm in thickness, respectively. Asshown in FIG. 3, a magnetic head 13 is disposed on a positive pressurecenter pad 14 located at the trailing edge of the slider 1. On the otherhand, a carbon overcoat 31 is formed on the magnetic disk 3 as well. Forthe purpose of preventing adhesion of the slider 1 and the magnetic disk3, the magnetic disk 3 has a texture on it. A texture 32 of the magneticdisk 3 is formed by etching the carbon overcoat. As for the shapethereof, it is formed more uniformly than the texture formed bywidespread tape processing. As for the concrete texture shape, the topportion of the texture 32 takes the shape of nearly a circle having adiameter of approximately 1 μm. The height d1 of the texture 32 isapproximately 15 nm, and the thickness d2 of the carbon overcoat 31 leftafter etching. processing is approximately 10 nm. The distance betweentexture w1 is approximately 10 μm. Therefore, the ratio of the area ofthe textures 32 to the area of the whole magnetic disk is approximately1%. Onto the carbon overcoat 31 of the magnetic disk, a lubricant isapplied with a thickness of approximately 2 to 4 nm.

In the case where slider 1 conducts the contact recording onto thismagnetic disk 3, the positive pressure center pad 14 of the slider 1,contacts the top portion of the texture 32 and the distance between onetexture and other texture is about 10 μm which is very narrow ascompared with the length of the slider 1. Therefore, the slider 1 cannotperfectly follow the shape of the texture and comes in contact with thetop portion of the texture 32 as it slides. In the case where the slider1 and the magnetic disk 3 maintain the contact state, the contact areaof the slider 1 is overwhelmingly smaller than that of the magnetic disk3 and the carbon layer 12 serving as the overcoat of the slider 1 wearsearlier than the carbon overcoat 31 of the magnetic disk 3.

FIG. 3 shows an example of the air bearing surface of the slider 1 usedin the first embodiment. The slider 1 has, a length of 1.2 mm and awidth of 1.0 mm. The air bearing surface includes one pair of positivepressure side pads 15 and 16 located on the leading edge of the slider1, one pair of positive pressure side pads 17 and 18 located on nearlythe central portion of the slider 1 in the length direction, and apositive pressure center pad 14 having a magnetic head 13 and located onthe trailing edge of the slider 1. A width of the positive pressurecenter pad 14 is wide enough to mount the magnetic head 13 thereon. Thewidth is 200 μm, for example, in the present invention. The leading edgeof this slider 1 has no tapered surfaces and all positive pressure padshave substantially smooth planar surfaces. The magnetic gap of themagnetic head 13 is formed at a distance of approximately 40 μm from thetrailing edge of the slider 1. The magnetic gap is formed so as toprevent the magnetic head 13 from coming in direct contact with themagnetic disk 3 in reading/writing operation. Furthermore, the magnetichead 13 is a composite head having an MR head and a thin film head. TheMR head utilizes a magneto resistive effect and serves as a read head.The thin film head serves as a write-head. A recess 19 for isolatingrespective positive pressure pads has a depth of at least 50 μm and isadapted so as, not to generate a negative pressure therein. The load wapplied by the suspension 2 is 500 mgf. The load point A is set so as tocoincide with the center of the slider 1.

An experiment of contact reading/writing was conducted by using theslider 1 and the magnetic disk 3 for 1,000 hours continuously. FIG. 4shows dependence of the wear of the carbon layer 12 formed on thepositive pressure center pad 14 of the slider 1 upon the contact forcef1 in this case. The contact force f1 was measured by a piezo sensorwhich is mounted on the slider 1. The wear value was normalized by awear value obtained after contact had been performed for 1,000 hourscontinuously under the state that the contact force f1 was kept at 500mgf equivalent to the load w. In order to change the contact force f1,the flying height of the slider 1 was changed diversely on a magneticdisk 3 having a texture height d1 of 15 nm or the texture height d1 ofthe magnetic disk 3 was changed diversely under the condition that theflying height of the slider 1 was constant. In the case where thecontact force f1 of the slider 1 and the magnetic disk 3 was 100 mgf orless, wear of the carbon overcoat 12 of the slider 1 was extremelysmall. If the contact force f1 became at least 100 mgf, the wear valueof the carbon overcoat 12 located at the trailing edge of the slider 1gradually increased. Until the contact force f1 reached approximately200 mgf, however, it could be observed that the carbon overcoat 12formed on the trailing edge of the slider 1 wore after continuouscontact state over 1,000 hours, but the wear debris did not stick to thepositive pressure pads 15 though 18 and the slider 1 could performflying/contact stably with respect to the magnetic disk 3 to the end.Reading and writing could be performed with no problem at all. At thistime, little wear could be observed on the top portion of the texture 32of the carbon overcoat of the magnetic disk 3 which is in contact withthe slider 1. This fact can be explained as follows. Immediately afterthe magnetic disk unit is started, the slider 1 is in contact with themagnetic disk 3 through a point or a line. As the wear of the carbonovercoat located on the trailing edge of the slider 1 advances, however,a newly generated surface of the carbon overcoat after wear becomes anew contact surface and consequently the contact pressure decreases.Until the contact force f1 reaches approximately 200 mgf, wear isconsidered not to advance if the area of contact is increased to somedegree. Furthermore, until the contact force f1 between the slider 1 andthe magnetic disk 3 reaches 200 mgf, the carbon overcoat is maintainedin the magnetic gap portion of the magnetic head 13 even aftercontinuous contact reading/writing operation lasting for 1,000 hours.The magnetic head 13 does not come in direct contact with the themagnetic disk 3. The phenomenon that the output of the MR head islowered due to heat generated by direct contact between the magnetichead 13 and the magnetic disk 3, i.e., the so-called thermal asperity isalso prevented.

FIG. 5 shows dependence of the contact force f1 between the slider 1 andthe magnetic disk 3 upon the maximum surface roughness of the magneticdisk 3. If the texture height d1 of the magnetic disk 3 is great andconsequently the maximum surface roughness of the magnetic disk 3 isgreat or if debris formed by defective processing, for example, ispresent on the magnetic disk 3, then the contact force generated whenthe slider 1 comes in contact with that portion becomes extremely greatand wear of the carbon overcoat of the slider 1 is caused from thatcontact portion, resulting in an accelerated damage. The texture heightd1 of the magnetic disk 3 in the first embodiment is approximately 15nm. Since the magnetic disk 3 itself has undulation, however, themaximum surface roughness is approximately 20 nm. For reducing thecontact force f1 less than 200 mgf, the maximum surface roughness isdesired to be 25 nm or less. This corresponds to the texture height d1of approximately 20 nm. On the other hand, if the maximum surfaceroughness of the magnetic disk 3 is in the mirrorlike state, a largefrictional force is generated in the contact portions of the slider 1and the magnetic disk 3 and the contact force f1 abruptly becomes large.Preferably, therefore, the maximum surface roughness is desired to be atleast 2 nm.

Furthermore, it is not necessary to form the carbon overcoat of theslider 1 on all of the positive pressure side pads 15 through 18 of theair bearing surface of the slider 1, but the carbon overcoat may beformed on the positive pressure center pad 14 of the trailing edge whichis in contact with the magnetic disk 3.

FIG. 6 is a graph showing the pressure distribution of the slider 1.When seen from the length direction of the slider 1, the positivepressure pads 17 and 18 opposite to the load point A are the largest ascompared with the positive pressure pads 15 and 16 and the positivepressure center pad 14 as shown in FIG.,1. In addition, the slider 1 hasno tapered surfaces on the leading edge. Even in the case where thetrailing edge of the slider 1 keeps in contact with the magnetic disk 3as in the present invention, therefore, the pressure center C resultingfrom the air flow is formed near the load point A. The distance L2between the load point A and the pressure center C is thus shortened,and the contact force f1 can be reduced. In the present embodiment, thedistance L1 between the load point A and the contact portion B was 0.5mm and the distance L2 between the load point A and the pressure centerC was 0.1 mm. Furthermore, since the slider 1 has such pressuredistribution that the pressure becomes the maximum under the load point,the stiffness of the air bearing in the pitch rotational direction issmall. This is also effective in reducing the contact force f1.

FIG. 7 shows dependence of the contact force f1 upon the sum of theslider mass and suspension equivalent mass when the magnetic disk 3having a texture height d1 of 15 nm and a maximum surface roughness of20 nm as described with reference to the first embodiment is used.Herein, the equivalent mass of the suspension 2 is a mass with which thesuspension 2 acts as effective inertia with respect to the movement ofthe slider 1 conducted in a direction perpendicular to the magnetic disksurface, and it is equivalent to a mass obtained when the suspension 2is approximated by a spring-mass model of a concentrated mass system.For making the contact force f1 equal to 200 mgf or less, it isnecessary to make the sum of the slider mass and the suspensionequivalent mass equal to 11 mg or less. In the first embodiment, the sumof equivalent masses of the combination of the slider 1 and thesuspension 2 was approximately 3 mg. For reducing the slider mass, it isnecessary to reduce the size of the slider. The size of the slider 1 isdesired to be at most approximately 2.0 mm in length and approximately1.0 mm in width. If the sum of the slider mass and the suspensionequivalent mass is too small, however, the load also becomes smallaccordingly and consequently handling becomes difficult in such a systemthat the slider 1 and the suspension 2 are separately formed as in thepresent invention. For facilitating handling, therefore, the sum of theslider mass and the suspension equivalent mass is preferably set equalto at least 2 mg.

As heretofore described, to reduce the contact force f1 reducing thesize of the slider 1 and increasing the distance L1 between the loadpoint A and the contact portion B are effective. However, they aremutually contradictory design parameters. Therefore, it is alsoimportant to reduce the load w to such a degree that the variance doesnot increase. Since the positive pressure pads of the slider 1 in thefirst embodiment has a substantially smooth surface and has no taperedsurfaces formed thereon, the load w can be minimized among the sliders 1having the same size. For making the contact force f1 equal to 200 mgfor less when the slider 1 in the first embodiment is used and reducingthe variance of the load w of the suspension 2, it is desired to set theload w equal to a value in the range of approximately 0.4 gf to 1.5 gf.

FIG. 8 shows the flying height profile, in the radial direction, of amagnetic disk having a diameter of 3.5 inch in the case where the slider1 of the first embodiment, the conventional positive pressure slider andthe conventional negative pressure slider are designed as flying typesliders. FIG. 9 shows the profile of the contact force. The contactforce is represented as a value obtained by normalizing the contactforce in each radial position by the contact force of each slider in aninner radius of the magnetic disk 3. The slider of conventional mixedflying/contact type has the following problem. When the position islocated at an outer radius, i.e., as the peripheral velocity isincreased, the flying force increases and the stable contact statecannot be maintained. In the slider according to the present invention,however, the flying height can be made nearly constant over the entiresurface of the magnetic disk as shown in FIG. 8. Therefore, the contactforce can also be kept constant over the entire disk surface whilekeeping the contact force at a sufficient small value with respect tothe wear of the carbon overcoat of the slider 1. The fact that thecontact force is kept at a nearly constant value over the entire disksurface means that stable contact reading/writing operation can beconducted over the entire disk surface. In the case of the conventionalpositive pressure slider, however, the velocity becomes greater andconsequently the flying height is increased when the position is locatedat an outer radius. As a result, the stable contact state cannot bemaintained in the case where the conventional positive pressure slideris used as the slider of a mixed flying/contact type.

Furthermore, in the case where the conventional negative pressure slideris used as the slider of a mixed flying/contact type, the negativepressure increases as the position moves to an outer radius. Therefore,the flying height profile can be made nearly constant in the same way asthe slider according to the present invention. Since the negativepressure becomes equivalent to the load w with respect to the magneticdisk, however, the contact force f1 becomes greater as the positionmoves to an outer radius. Thus the risk of occurrence of a fatal damagebetween the slider and the magnetic disk becomes greater.

Further features of a second embodiment will now be described byreferring to FIGS. 10A and 10B. In the magnetic disk unit of the contactrecording type as in the present invention, not only does a staticcontact force f1 steadily act on the contact portion B between theslider 1 and the magnetic disk 3 as described before with reference tothe first embodiment, but a dynamic impulsive force P which ishigh-frequency disturbance on the slider 1 from the magnetic disk 3 viathe contact portion B is also present. By this impulsive force P,impulsive force T acts on the suspension 2 from the slider 1 via theload point A. As a reaction thereof, the slider 1 receives the impulsiveforce T from the suspension 2. By the impulsive force T acting from thesuspension 2 on the slider 1 via the load point A, unsteady contactforce in the contact portion B between the slider 1 and the magneticdisk 3 increases. Or the slider 1 which has been in contact with themagnetic disk 3 is temporarily separated from the magnetic disk andthereafter hits the magnetic disk 3 again. This is called a jumpingphenomenon. This results in a problem that the magnetic disk 3 isdamaged fatally and reading/writing operation becomes impossible.

In reducing such trouble caused by a dynamic impulsive force, it iseffective to dispose the load point A on a point which lies between theleading edge of the slider 1 and the center of the slider lengthdirection as in the present embodiment. This effect will now bedescribed in detail by referring to FIG. 10B. FIG. 10B shows dependenceof the impulsive force T acting between the slider 1 and the suspension2 via the load point A when the impulsive force P has acted on thecontact portion B of the trailing edge of the slider 1, upon thedistance x between the leading edge of the slider 1 and the load pointA. When x=L, the load point A and the contact point B between the slider1 and the magnetic disk 3 are on the same axis of the slider thicknessdirection, and the impulsive force P acting between the slider 1 and themagnetic disk 3 becomes equal to the impulsive force T acting betweenthe slider 1 and the suspension 2. When x=0.5L, i.e., when the loadpoint A is located on the center of the slider length direction and theload point A and the center of gravity of slider G are on the same axisof the slider thickness direction, the impulsive force P becomes equalto the impulsive force T. On the other hand, when 0.5L<x<L, i.e., whenthe load point A is located on the trailing edge of the slider 1 withrespect to the center of the slider length direction, the impulsiveforce T which is greater than the impulsive force P acts between theslider 1 and the suspension 2. This increases the possibility that theslider 1 will hit the magnetic disk 3 with an impulsive force greaterthan the impulsive force P which has acted initially at the contactpoint B and the magnetic disk 3 will be damaged fatally. On thecontrary, when 0.5L>x, i.e., when the load point A is located on theleading edge side of the slider 1 with respect to the center of theslider length direction, the impulsive force T acting between the slider1 and the suspension 2 becomes smaller than the impulsive force actingbetween the slider 1 and the magnetic disk 3 and consequently thepossibility of damaging the magnetic disk fatally is also decreased.Preferably, by letting 0.42L>x, the magnitude of the impulsive force Tacting between the slider 1 and the suspension 2 can be made equal tohalf or less of the magnitude of the impulsive force P acting betweenthe slider 1 and the magnetic disk 3. In particular, when x=(⅓)L, therelation T=0 is satisfied and an impulsive force P which has actedbetween the slider 1 and the magnetic disk 3 on the contact portion B isnot transmitted to the suspension 2 via the load action point A, thusthere being no impulsive force from the suspension on the slider 1. Onthe contrary, even if any disturbance acts on the suspension 2, it isnot transmitted to the contact portion B between the slider 1 and themagnetic disk 3 via the load point A. By thus making the contact portionB and the load point A mutual centers of impact with the center ofgravity of slider G between, mechanical interaction in the verticalmovement direction is not present between the contact portion B and thesuspension 2 and mutual isolation of disturbance can be performed. Inaddition, by displacing the load point A to the leading edge side ofslider 1 with respect to the slider length direction, the distance L1between the load point A and the contact portion B becomes great asevident from equation (3) and the steady contact force f1 can also bereduced simultaneously.

In reducing the jumping of the slider 1 from the magnetic disk 3 causedby contact between the slider 1 and the magnetic disk 3 and reducingincrease of unsteady contact force caused thereby, it is effective tonot only adopt the above described mechanical disturbance isolatingmethod but also to apply high polymer materal such as polyimide onto thesuspension 2 as a vibration isolating material. Mounting a vibrationisolating material on the suspension 2 has been performed in the case ofthe flying type as well. In a system such as the contact recording typein which high-frequency distribution is expected, however, the abovedescribed vibration isolating material of the suspension functionsfurther effectively.

Furthermore, as another method for reducing the unsteady contact force,it is effective to reduce the mass of the slider. For example, onemethod is to cut the recess portion located around the positive pressurecenter pad 14 as shown in FIG. 12 to reduce the mass of the slider 1.

FIG. 10C is a side view illustrating the contact state between theslider 1 and the magnetic disk 3 in a magnetic disk unit of the contactrecording type according to the second embodiment of the presentinvention. FIG. 11 shows an example of the air bearing surface of theslider 1 in the second embodiment. The slider 1 has a length of 1.2 mmand a width of 1.0 mm. The air bearing surface of slider 1 includes onepair of positive pressure pads 171 and 181 formed in positions oppositeto the load point A, and a positive pressure center pad 14 having amagnetic head 13 and located on the trailing edge. The depth of therecess 19 is at least 50 μm and a negative pressure is not generated.The load w given by the suspension 2 via the load point A is 500 mgf.This load w is nearly equal in magnitude to flying force f2 generated bythe positive pressure pads 171 and 181. Furthermore, the pressure centerC of the flying force f2 is made nearly the same as the load actionpoint A. In addition, flying force generated by the positive pressurecenter pad 14 of the slider 1 is negligibly small as compared with theflying force f2. In the present embodiment, the load point A is locatedon the leading edge side with respect to the center of the slider.Therefore, the distance L1 between the load point A and the positivepressure center pad 14 is sufficiently bigger than the distance betweenthe load point A and the pressure center G of the flying force f2generated by the positive pressure pads 171 and 181. Furthermore, thegreatest feature of the present embodiment is that moment Mp in such adirection as to thrust the positive pressure center pad 14 against themagnetic disk 3 acts on the slider 1 by not only applying the load wupon the load point A but also turning a gimbal 21 of the suspension 2by an angle 9 in such a direction as to make the positive pressurecenter pad 14 approach the magnetic disk 3. In other words, a gimbalhaving much smaller stiffness than that of the loadbeam portion of thesuspension 2 is used to add the load f1 to the positive pressure centerpad 14. A very small contact load has thus been realized by using asimple configuration.

Equilibrium of force exerted between the slider/suspension and themagnetic disk in the second embodiment can be expressed by the followingequations.

w≈f 2  (4)

$\begin{matrix}{{f1} = \frac{Mp}{L1}} & (5)\end{matrix}$

In the second embodiment, stiffness kp of the gimbal 21 in the pitchdirection was set equal to 0.087 gf·mm/degree, and the distance L1between the load point A and the contact portion B of the positivepressure center pad 14 was set equal to 0.8 mm. In thisslider/suspension, the contact force f1 can be set equal to 200 mgf, forexample, by tilting the pitch angle θ by 1.83° beforehand in such adirection as to make the positive pressure center pad 14 approach themagnetic disk 3. Processing of such a degree can be easily implemented.

FIG. 13 is a side view illustrating the contact state between theslider/suspension and the magnetic disk in a magnetic disk unit ofcontact recording type according to a third embodiment of the presentinvention. FIG. 14 shows an example of the slider in the thirdembodiment. In the slider/suspension of the third embodiment, the sliderflies in such state that the load w balances with the flying force f2generated by the positive pressure pads 171 and 181 in the same way asthe slider/suspension of the second embodiment. The positive pressurecenter pad 14 is subjected to a force equivalent to load f1 caused bythe moment of the gimbal 21 and it is in contact with the magnetic disk.In the third embodiment, a positive pressure rail 191 for generatingnegative pressure on the leading edge side of the positive pressurecenter pad 14 and a negative pressure recess 192 in which negativepressure is generated are formed as shown in FIG. 14 unlike the secondembodiment. The recess 19 has a depth of at least 50 μm in the same wayas the first and second embodiments and generates only positivepressure. The negative pressure recess 192 has a depth of approximately6 μm. In the present embodiment, design is performed so that the flyingforce in this positive pressure rail 191 will be equal in magnitude tothe negative pressure generated in the negative pressure recess 192.Therefore, the flying force generated by this positive pressure rail 191and the negative pressure generated by the negative pressure recess 192do not affect the magnitude of the flying force and contact force of theentire slider. However, if the positive pressure rail 191 and thenegative pressure recess 192 are disposed on the air bearing surface ofthe slider 1 and air is effectively disposed between the slider and themagnetic disk, dumping of air is increased. Especially in the magneticdisk unit of contact recording type as in the present invention, thisair dumping effectively restricts vibration of the slider/suspension.

FIG. 15 is a top view of a magnetic disk unit with rotary actuatorscheme to which the above described configuration according to thepresent invention is applied. The slider 1 according to the presentinvention is subjected to seeking and positioning on whole data track ofthe magnetic disk 3 by a rotary actuator arm 4 via a suspension 2. Therotary actuator arm 4 is driven by a voice coil motor 5 in a directionrepresented by arrow D. With respect to magnetic head positioning, themost noticeable difference between the magnetic disk unit of the contactrecording type according to the present invention and the conventionalslider/suspension of flying type is that frictional force f_(cr2) actsbetween contact points of the slider and the magnetic disk in adirection opposite to the positioning movement direction at the time ofseeking and positioning. This frictional force f_(cr2) exerts greatinfluence upon the positioning precision of the magnetic head. If thefrictional force becomes great, then the magnetic-head gets out of thedata track in which the magnetic head should be positioned andreading/writing cannot be conducted. In the worst case, the actuatormight run away and the slider/suspension or the magnetic disk might bedestroyed. This frictional force f_(cr2) in the seeking and positioningdirection is defined by lateral stiffness k₂ of the suspension in theseeking and positioning direction and data track width T_(r) asrepresented by the following expression.

 f _(cr2) ≦k ₂ ·T _(r)  (6)

Assuming that the track density is 20,000 TPI tracks/inch), the trackwidth T_(r) is 1.27 μm. The lateral stiffness k₂ of the suspensionaccording to the present invention in the seeking and positioningdirection is approximately 0.24 kgf/mm, and the frictional force f_(cr2)in the seeking and positioning direction becomes approximately 300 mgf.For preventing the magnetic head from getting out of the data track inwhich the magnetic head should be positioned, therefore, it is at leastnecessary to make the frictional force f_(cr2) less than 300 mgf. If itis desired to increase the track density, it is necessary to increasethe lateral stiffness k₂ of the suspension 2 or reduce the frictionalforce f_(cr2) itself. Denoting the coefficient of friction between theslider 1 and the magnetic disk 3 by μ., load by w, and adsorptionbetween the slider 1 and the magnetic disk 3 by w_(s), the frictionalforce f_(cr2) can be represented by the following expression as well.

f _(cr2)≦μ(w+w _(s))  (7)

According to experiments conducted by the present inventors, thecoefficient of friction between the slider 1 of the present inventionand the magnetic disk having the texture height d1 described withreference to the first embodiment was approximately 0.3. The load w ofthe suspension 2 is 500 mgf For setting f_(cr2) equal to 300 mgf or lessas described above, therefore, the adsorption w_(s) must be 500 mgf orless from expression (7). At the time of seeking and positioning, thepositive pressure center pad 14 is in contact with the magnetic disk 3and the area of that contact is approximately 0.02 mm2. Therefore,adsorption allowed per unit area of the contact portion B is 25 gf/mm².This is nearly equal to adsorption acting between the slider 1 and themagnetic disk 3 per unit area in the case where the magnetic diskdescribed with reference to the first embodiment having a texture heightd1 of 15 nm and a texture area ratio of 1% is used. Therefore, it isappreciated that the magnetic disk having the configuration describedwith reference to the first embodiment is effective in reducing thefrictional force f_(cr2) in the seeking direction as well.

Furthermore, when a slider/suspension of the contact recording type asin the present invention is recording on the same radius of a magneticdisk, or during seeking and positioning operation, frictional forcef_(cr3) acts in the bit direction (circumference direction) of themagnetic disk. Unless this frictional force f_(cr3) in the bit directionalso satisfies a condition similar to that of the frictional forcef_(cr2) in the track direction (radius direction), precise positioningcannot be conducted. Denoting lateral stiffness in the bit direction,which is octagonal D to the seeking direction, of the suspension by k₃and bit width by T_(b), the following expression must thus be satisfied.

f _(cr3) ≦k ₃ ·T _(b)  (8)

Assuming now that the bit density is 500,000 BPI (bits/inch), the bitwidth becomes 0.05 μm. If the frictional force f_(cr3) in the bitdirection is desired to be nearly equal to frictional force f_(cr2) inthe seeking direction, the stiffness k₃ in the bit direction must be setequal to approximately 6 kgf/mm.

In the slider/suspension of the flying type, texture processing isconducted on the magnetic disk in order to reduce the frictional forceat the time of starting. In the magnetic disk unit of contact recordingtype, however, the texture of the magnetic disk is important to reducethe frictional force not only at the time of starting but also at thetime of seeking.

In the above described embodiment, texture processing is conducted onthe magnetic disk side. Even if texture processing is conducted in theslider 1 side, however, a similar effect can be obtained. At this time,the magnetic disk 3 need not undergo texture processing, and themagnetic recording gap can be advantageously reduced by a valuecorresponding to the texture height d1.

As heretofore described, the contact force between the slider 1 and themagnetic disk 3 can be made 200 mgf or less in the slider of mixedflying/contact type according to the present invention. In addition,contact reading/writing operation can be conducted stably over theentire surface for a long time without depending upon the velocity.Furthermore, disturbances acting on the slider 1 or the suspension 2 canbe isolated each other. It is also possible to prevent jumping of theslider 1 from the magnetic disk 3 and increasing of unsteady contactforce. Furthermore, the contact force at the time of seeking andpositioning can be reduced, and accurate positioning can be conductedeven in contact recording.

What is claimed is:
 1. A magnetic disk unit comprising: a magnetic diskattached to a spindle so as to be rotatable; a slider which has a firstpad and second pads, and said first pad, which stays in contact withsaid magnetic disk, has a magnetic head for reading/writing dataonto/from said magnetic disk and is located substantially in a center ofsaid slider in a width direction; a suspension which provides saidslider with a predetermined load; a gimbal coupled to said suspension;an actuator arm which positions said slider attached to said suspensionon said magnetic disk; and a positive pressure rail for generatingnegative pressure on the leading edge side of the first pad; wherein,the positive pressure rail having an open side, and partiallysurrounding a negative pressure recess formed to generate negativepressure; wherein a magnitude of a flying force generated by saidpositive pressure rail is substantially equal to a magnitude of thenegative pressure generated by said negative pressure recess; whereinsaid slider being provided a pitch moment in such a direction as to makesaid first pad approach said magnetic disk; wherein said pitch momentbeing generated by said predetermined load upon a load point of saidsuspension with respect to said slider.
 2. The magnetic disk unitaccording to claim 1, wherein said second pads are separated from saidmagnetic disk to fly by an air flow caused by rotation of said magneticdisk, and when said slider is seek positioned on a certain track on saidmagnetic disk by said actuator arm via said suspension, frictional forceexerted between said first pad and said magnetic disk is smaller than aproduct of lateral stiffness of said suspension in a seek positioningdirection and a track width.
 3. The magnetic disk unit according toclaim 1, wherein when positioning is conducted continuously on a sametrack on said magnetic disk while a contact state between said first padand said magnetic disk is being maintained, frictional force exertedbetween said first pad and said magnetic disk is smaller than a productof lateral stiffness of said suspension in a bit direction and a databit width on said magnetic disk.
 4. The magnetic disk unit according toclaim 1, wherein a load point on said suspension is positioned between aleading edge of said slider and a position located at a distanceequivalent to substantially 0.42 times a whole length of said sliderfrom a leading edge of said slider, said load point being matched with acenter of impact in contacting said first pad with said magnetic disk,so that a moment acts on said slider by applying a predetermined loadupon a load point and also turns said gimbal by a predetermined angle ina direction so as to move said first pad towards said magnetic disk. 5.The magnetic disk unit according to claim 1, wherein said load point ofsaid suspension with respect to said slider is in a position located ata distance equivalent to substantially one third of a whole length ofsaid slider from a leading edge of said slider, wherein a center ofimpact in contacting said first pad to said magnetic disk is located ata same position as said load point and defined by a shape of saidslider.
 6. The magnetic disk unit according to claim 1, wherein saidfirst pad includes a carbon overcoat having a thickness of 7 nm or less.7. The magnetic disk unit according to claim 1, wherein a maximumroughness of a surface of said magnetic disk is equal to 3 nm or moreand 25 nm or less.
 8. The magnetic disk unit according to claim 1,wherein a sum of a mass of said slider and an equivalent mass of saidsuspension is at least 2 mg and at most 11 mg.
 9. A magnetic disk unitaccording to claim 1, wherein said pitch moment being provided by saidpredetermined load upon the load point of said suspension with respectto said slider and by a predetermined angle of turning said gimbal withrespect to said suspension.
 10. A magnetic disk unit comprising: amagnetic disk attached to a spindle so as to be rotatable; a sliderwhich has a first pad and second pads, and said first pad, whichcontacts with said magnetic disk, has a magnetic head forreading/writing data onto/from said magnetic disk; a suspension whichprovides load to said slider; a gimbal coupled to said suspension; anactuator arm which positions said slider attached to said suspension onsaid magnetic disk; and a positive pressure rail for generating negativepressure on the leading edge side of the first pad; wherein the positivepressure rail having an open side, and partially surrounding a negativepressure recess formed to generate negative pressure; wherein amagnitude of a flying force generated by said positive pressure rail issubstantially equal to a magnitude of said negative pressure generatedby said negative pressure recess; wherein said slider being provided apitch moment in such a direction as to make said first pad approach saidmagnetic disk; wherein said pitch moment being generated by said loadupon a load point of said suspension with respect to said slider. 11.The magnetic disk unit according to claim 10, wherein said second padsare separated from said magnetic disk to fly by an air flow caused byrotation of said magnetic disk, and when said slider is seek positionedon a certain track on said magnetic disk by said actuator arm via saidsuspension, frictional exerted between said first pad and said magneticdisk is smaller than product of lateral stiffness of said suspension ina seek-positioning direction and a track width.
 12. The magnetic diskunit according to claim 10, wherein when positioning is conductedcontinuously on the same track on said magnetic disk while an contactstate between said first pad and said magnetic disk is being maintained,frictional force extended between said first pad and said magnetic diskis smaller than product of lateral stiffness of said suspension in a bitdirection and a data bit width on said magnetic disk.
 13. The magneticdisk unit according to claim 10, wherein a load point on said suspensionpositioned between a leading edge of said slider and a position locatedat a distance equivalent to substantially 0.42 times a whole length ofsaid slider from the leading edge of the slider, so that a moment actson said slider by applying a load upon a load point and also turns saidgimbal by a predetermined angle in a direction as to move said first padtowards said magnetic disk.
 14. The magnetic disk unit according toclaim 10, wherein said load point of said suspension with respect tosaid slider is in a position located at a distance equivalent tosubstantially one third of the whole length of said slider from saidleading edge, wherein a center of impact in contacting said first pad tosaid magnetic disk is located at the same position as said load pointand defined by a shape of said slider.
 15. The magnetic disk unitaccording to claim 10, wherein said first pad includes a carbon overcoathaving a thickness of 7 nm or less.
 16. The magnetic disk unit accordingto claim 10, wherein the sum of the mass of said slider and anequivalent mass of said suspension is at least 2 mg and at most 11 mg.17. The magnetic disk unit according to claim 10, wherein said first padis located substantially in a center of said slider in a widthdirection.
 18. A magnetic disk unit according to claim 10, wherein saidpitch moment being provided by said load upon the load point of saidsuspension with respect to said slider and by a predetermined angle ofturning said gimbal with respect to said suspension.
 19. A magnetic headgimbal assembly comprising: a slider having a first pad and second pads,and said first pad, which contacts with a magnetic disk, has a magnetichead for reading and writing data onto and from said magnetic disk; asuspension for providing the slider, a proximal portion of which isattached to an actuator arm of an actuator for positioning the slider ofthe magnetic disk; a gimbal coupled to said suspension; and a positivepressure for generating negative pressure on the leading edge side ofthe first pad; wherein said positive pressure rail having an open sideand partially surrounding a negative pressure recess formed to generatenegative pressure; wherein a magnitude of a flying force generated bysaid positive pressure rail is substantially equal to magnitude of saidnegative pressure generated by said negative pressure recess.
 20. Themagnetic head gimbal assembly according to claim 19, wherein said secondpads are separated from said magnetic disk to fly by an air flow causedby rotation of said magnetic disk, and when said slider is seekpositioned on a certain track on said magnetic disk by said actuator armvia said suspension, frictional exerted between said first pad and saidmagnetic disk is smaller than product of lateral stiffness of saidsuspension in a seek positioning direction and a track width.
 21. Themagnetic head gimbal assembly according to claim 19, wherein whenpositioning is conducted continuously on the same track on said magneticdisk while an contact state between said first pad and said magneticdisk is being maintained, frictional force exerted between said firstpad and said magnetic disk is smaller than product of lateral stiffnessof said suspension in a bit direction and a data bit width on saidmagnetic disk.